FIG. 1 is a diagram illustrating a signal flow for a network entry procedure of an MS in a legacy Institute of Electrical and Electronics Engineers (IEEE) 802.16e network.
Referring to FIG. 1, the MS receives DownLink (DL)-MAP, DL Channel Descriptor (DCD), UpLink (UL)-MAP, and UL Channel Descriptor (UCD) messages from a BS and acquires DL and UL parameters from the received messages in step 110.
In step 111, the MS adjusts its timing offset and power-related parameter by initial ranging to the BS.
Upon receipt of a UL-MAP message including information about an initial ranging interval allocated to the MS, the MS randomly selects one of initial ranging codes and transmits the selected initial ranging code to the BS on the uplink during the initial ranging interval.
The MS and the BS can adjust UL transmission parameters of the MS by repeatedly exchanging a ranging code and a Ranging Response (RNG-RSP) message between them. If the UL transmission parameters are successfully adjusted, the BS transmits a code indicating success in an RNG-RSP message to the MS. Here, the BS allocates non-contention-based UL resources to the MS by a predetermined UL-MAP Information Element (IE) so that the MS can transmit a Ranging Request (RNG-REQ) message.
The MS transmits an RNG-REQ message including its Media Access Control (MAC) address using the allocated UL resources. Upon receipt of the RNG-REQ message, the BS transmits an RNG-RSP message to the MS, in order to allocate a basic Connection Identifier (CID) and a primary CID to the MS.
In step 112, the MS performs basic capabilities negotiation with the BS. The MS transmits supported parameters, that is, information about the capabilities of the MS to the BS and receives a response for the transmitted parameters from the BS during the basic capabilities negotiation of step 112.
The MS performs authorization and exchanges security keys with the BS in step 113. Then the MS registers to the BS in step 114 and performs authentication with an Authentication, Authorization and Accounting (AAA) server in step 120.
Finally, the MS transmits a Dynamic Service Add Request (DSA-REQ) message to and receives a Dynamic Service Add Response (DSA-RSP) message from the BS to establish a service flow with the BS in step 122.
Conventionally, it is defined that when a BS restarts during a normal operation, MSs perform network entry to the BS, recognizing the BS's restart. In case of a BS restart triggered by a serious error or an operator's intention, the BS transmits a BS Restart Count incremented by 1 to the MSs by a DCD message (every 10 s at maximum).
Table 1 below describes the definition of Restart Count in a DCD message in IEEE 802.16Rev2.
TABLE 1TypePHYName(1 byte)LengthValue (variable length)scopeBS Restart1541BS Restart Count is incrementedAllCountby 1 whenever the BS restarts.The value ranges from 0 to 255.
Each time the BS restarts, it increments the Restart Count by 1. After receiving the DCD message, the MSs compare a previous BS Restart Count with a current BS Restart Count and determine whether the BS has restarted. If the BS has restarted, that is, if the current BS Restart Count is larger than the previous BS Restart Count, the MSs re-register to the BS by network entry. The received current BS Restart Count is stored in the MSs.
A Mobile Neighbor Advertisement (MOB_NBR-ADV) message (every 30 s at maximum) delivers Restart Counts of neighbor BSs. The MSs also store the Restart Counts of the neighbor BSs to perform the above-described operation during handover.
The BS restart caused by a serious errors or an operator's intention does not occur frequently. Even though the BS restarts due to a serious error or an operator's intention, the interval between such BS restarts is not short. Assuming that a serious error occurs every three days, the DCD message is transmitted 25,920 times and the MOB_NBR-ADV message is transmitted 8,640 times.
Accordingly, the BS transmits Restart Counts of 103,680 bytes (DCD: 77,760 bytes (3 bytes×25920) and MOB_NBR-ADV: 25,920 bytes (3 bytes×8640) in order to command network entry to the MSs. If there are two or more neighbor BSs, the MOB_NBR-ADV message carries more bytes according to the number of the neighbor BSs.
Thus, it is inefficient to transmit a restart-related parameter by a periodic message such as a DCD message or a MOB_NBR-ADV message.